The present invention relates to an exhaust pipe for motor vehicle muffler, and more particularly to such an exhaust pipe, which prevents outside cold air from being sucked into the exhaust pipe to cause a vibration and resonance when the accelerator pedal is released.
Motorcycles and cars are the requisite transportation vehicles to most people for the advantages of high convenience and comfort. A motor vehicle has an exhaust pipe to guide exhaust gas from the engine to the outside air, and a muffler mounted on the exhaust pipe to soften sound. The performance of the exhaust pipe of a motor vehicle greatly affects the performance (horsepower) of the engine. However regular exhaust pipes are still not satisfactory in function. As illustrated in FIG. 5, the exhaust pipe B has a plurality of muffling holes spaced around the periphery within the muffler A. When passing through the exhaust pipe, a part of exhaust gas rushes out of the muffling holes on the exhaust pipe B into the space within the muffler A around the outside wall of the exhaust pipe B to soften sound. This design of exhaust pipe has numerous drawbacks. Because the exhaust pipe is a straight pipe, the major part of exhaust gas directly flows out of the exhaust pipe, and only a small amount of exhaust gas rushing out of the muffling holes. The currents of exhaust gas which rushed out of the muffling holes on the exhaust pipe directly strike the inside wall of the muffler, causing noises. Further, when the driver releases the accelerator pedal, outside cold air will be sucked into the exhaust pipe, causing a resonance and vibration. FIG. 6 shows another structure of exhaust pipe according to the prior art. This structure of exhaust pipe is formed of two spiral pipe portions of different diameters, and has a plurality of muffling holes spaced over the periphery of the spiral pipe portions. The spiral pipe portions simply turn exhaust gas into a spiral flow, however they can not accelerate the velocity of exhaust gas. When exhaust gas rushing out of the muffling holes, it directly strikes the inside wall of the muffler, causing noises.
The present invention has been accomplished to provide an exhaust pipe, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide an exhaust pipe, which accelerates the velocity of exhaust gas which turning exhaust gas into a spiral flow. It is another object of the present invention to provide an exhaust pipe, which prevents outside cold air from being sucked into the exhaust pipe when the accelerator pedal is released. To achieve these and other objects of the present invention, there is provided an exhaust pipe, which comprises a plurality of muffling holes arranged over the periphery, a partially perforated conical tube suspended on the inside an axially extended from the exhaust gas input end thereof for accelerating exhaust gas passing through, and a plurality of spiral portions formed integral with the periphery thereof and spaced around the conical tube for turning exhaust gas escaped from peripheral through holes on the conical tube into a spiral flow and for causing a vacuum to suck escaped exhaust gas from the space within the muffler around the exhaust pipe into the exhaust pipe again.